Yard MD Blog: Invasive giant hogweed and its native lookalike

If you are unsure which is which, its best to avoid them all

Jun. 19, 2014

Both native cow parsnip, shown here, and invasive giant hogweed, are members of the carrot family that bloom with huge clusters of white flowers at the tips of the stalks. If you aren't sure which plant you are dealing with, avoid contact altogether. The juices of these plants, like wild parsnip, can cause severe burning and blistering when exposed to bare skin and sunlight. / Rob Zimmer/Post-Crescent Media

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Post-Crescent Media

In yesterday’s blog I began our look at members of the carrot or parsnip family with those that bloom in yellow.

In white, the dangerous, toxic giant hogweed is a massive plant that has not yet become fully established in our state. Only discovered in a few small patches in two Wisconsin counties, giant hogweed is not as widespread as its cousin, the yellow-blooming wild parsnip, but is just as toxic.

Unfortunately, true giant hogweed is often confused with native cow parsnip, an equally large, native plants with similar white flower clusters at the tip of each stalk.

Currently, giant hogweed has only been observed in two counties in our area, Iron County and Manitowoc County. Cow parsnip, which again is a native plant and much more benign, is widespread and often occurs along area ditches, railways and forest edges.

Distinguishing the two is somewhat difficult, though cow parsnip is somewhat smaller. Even so, how parsnip can easily reach 6 to 8 feet in height. Giant hogweed can easily reach 8 to 10 feet or higher. The leaves of cow parsnip are solid green, while those of giant hogweed are somewhat mottled in appearance. Both have huge, flat clusters of white flowers on the tips of the stalks that may reach a foot across or more.

If you are not certain whether something is giant hogweed or cow parsnip, it is best to leave the plant alone. Do not take a risk coming into contact with the harmful juices of hogweed, which can cause a reaction similar to that of wild parsnip. This includes burning, blistering and rashes as the juices on exposed skin come into contact with ultraviolet light. In some cases, the reaction with giant hogweed can be even more severe.

Cow parsnip, while native, can cause a similar reaction in some cases.

Make an effort to familiarize yourself with each of these plants to be able to identify them. This protects you from the harmful invasives, as well as keeping the harmless natives safe and secure. We should not be persecuting native plants just because they look similar to invasive plants.

In addition to the four species described here, there are other members of this family, some of which are invasive and dangerous than some of which are harmless. The whole celery/carrot family includes hundreds of different plants.

Examples of others include harmless, but invasive Queen Anne’s lace and poisonous water hemlock. If in doubt, simply leave them all alone.

The biggest danger of these plants comes from getting the juices or sap on bare skin. Once exposed, symptoms appear in about 24-48 hours.